The config validation code repeated the same nil-check-before-dereference pattern ~5 times across validation_gateway.go and validation_server.go, with no shared abstraction — increasing bug risk (forgetting the nil guard on new fields) and making the validation functions harder to scan.

Changes

• validation_rules.go — Adds validateOptionalInt(ptr *int, logMsg string, validateFn func(int) *ValidationError) error. Explicitly checks *ValidationError != nil before returning as error to avoid the typed-nil-interface pitfall.

• validation_gateway.go — Replaces 4 nil-guarded blocks (Port, StartupTimeout, ToolTimeout, PayloadSizeThreshold) with validateOptionalInt calls.

• validation_server.go — Replaces the per-server ToolTimeout nil-guard. The zero-means-inherit sentinel is handled inside the closure, preserving existing semantics.

• validation_rules_test.go — Adds TestValidateOptionalInt covering: nil ptr (no-op), valid value, invalid value, closure with zero-sentinel guard.

Example

// Before (repeated ~5×):
if gateway.StartupTimeout != nil {
    logValidation.Printf("Validating startup timeout: %d", *gateway.StartupTimeout)
    if err := TimeoutPositive(*gateway.StartupTimeout, "startupTimeout", "gateway.startupTimeout"); err != nil {
        return err
    }
}

// After:
if err := validateOptionalInt(gateway.StartupTimeout, "Validating startup timeout",
    func(v int) *ValidationError { return TimeoutPositive(v, "startupTimeout", "gateway.startupTimeout") }); err != nil {
    return err
}

Adding a new optional *int field now requires a single validateOptionalInt call rather than a copy-pasted nil-guard block.

• Fixes [duplicate-code] Duplicate Code Pattern: Optional Pointer Field Validation Guard in Config #10044